This invention relates to a method of using bone morphology data to design a family of prosthetic hip implants.
The femoral fit of a prosthetic hip stem component is a key factor for the long term success of a cementless total hip replacement. Traditionally, hip stems have been designed based on predicate clinical data and limited bone morphology data. Numerous studies have analyzed the femur bone morphology. For example, (1) Noble et al., Clinical Orthopaedics and Related Research, 1988; (2) Husmann et al., Journal of Arthoplasty, 1997; (3) Laine et al., Journal of Arthoplasty, 2000; (4) Dorr et al., Bone, 1993; (5) Khang et al., Clinical Orthopaedics and Related Research, 2003; (6) Bo et al., Journal of Orthopaedic Science, 1997. However, a method to utilize bone morphology data for new implant designs has not been developed.
Because bone geometries vary from person to person (and may also vary with age), typical orthopeadic implants are often offered as part of a set or series of different sized implants. Typically, implant sets are created by first designing one size of implant and then scaling that implant in a proportional manner to define the geometries of the other implant sizes (e.g., increasing the width of the elongated insertion region by a uniform amount along the entire length of the stem).
Typical implant system growth does not accurately reflect the geometries of different bone sizes. Larger femurs, for example, are not simply bigger versions of smaller femurs. For instance, it has been discovered that proximal portions of the medullary canal (some or all of which may be referred to as the metaphysis) may “grow” at a greater rate than distal portions (some or all of which may be referred to as the diaphysis) as femoral size increases. Thus, femoral hip stem sets that grown the proximal portion at the same rate as the distal portion from size to size do not necessarily reflect the actual geometries of the various sizes of femurs. Thus, implant sets made in accordance with traditional methodologies may, in some cases, fit poorly when installed, and may lead to implant failure for the reasons discussed above or for other reasons.
U.S. Pat. No. 7,749,278 discloses a hip stem family which has a constant medial portion and an increasing lateral portion (see FIG. 1A).
This invention describes a method to systematically utilize bone morphology data for the development of new hip implant designs. The method is defined in seven (7) steps. (see FIG. 1C.)